Supramolekulare Selbstorganisation von bidirektionalen Kaskadenmolekülen: Automorphogenese

Hydrogen-Bonded Dendronized Polymers and Their Self-Assembly in Solution

Frechet-type benzyl ether dendrons of second and third generations with a carboxyl group (G2, G3) at the apex site could attach to poly(4-vinylpyridine) (PVP), forming hydrogen-bonded dendronized polymers (HB denpols) in their common solvent, chloroform. The HB denpols show unique self-assembly behavior, forming vesicles in the common solvent under ultrasonic treatment. The structure and morphology of the vesicles were characterized by dynamic light scattering (DLS), static light scattering (SLS), SEM, TEM, and AFM. The size of the vesicles decreases and the thickness of the vascular membrane increases as the molar ratio of Gx/PVP increases. The hydrogen bonding, pi-pi aromatic stacking of the dendrons, and the considerable difference in architecture between the dendron Gx and PVP are the main factors facilitating the assembly of the HB denpols in the common solvent.

Self-Organisation in the Assembly of Gels from Mixtures of Different Dendritic Peptide Building Blocks

This paper investigates dendritic peptides capable of assembling into nanostructured gels, and explores the effect on self-assembly of mixing different molecular building blocks. Thermal measurements, small angle X-ray scattering (SAXS) and circular dichroism (CD) spectroscopy are used to probe these materials on macroscopic, nanoscopic and molecular length scales. The results from these investigations demonstrate that in this case, systems with different "size" and "chirality" factors can self-organise, whilst systems with different "shape" factors cannot. The "size" and "chirality" factors are directly connected with the molecular information programmed into the dendritic peptides, whilst the shape factor depends on the group linking these peptides together--this is consistent with molecular recognition hydrogen bond pathways between the peptidic building blocks controlling the ability of these systems to self-recognise. These results demonstrate that mixtures of relatively complex peptides, with only subtle differences on the molecular scale, can self-organise into nanoscale structures, an important step in the spontaneous assembly of ordered systems from complex mixtures.

Structural Diversity of α-Amino Acid Based Layer-Block Dendrons and Their Layer-Block Sequence-Dependent Gelation Properties

A library of G1-G3 alpha-amino acid based layer-block dendrons 1-6 containing different amino acid residues in the different concentric layers was prepared by solution-phase peptide synthesis. The structures of these dendrons were characterized by 1H and 13C NMR spectroscopy and, except for the G3 series of compounds, by mass spectrometry. The purities of these compounds were also determined by size-exclusion chromatography. Owing to the presence of a large number of amide groups, these dendrons exhibit unusually strong self-aggregating properties in both polar and nonpolar solvents. Some of these dendrons are found to be extremely good organogelators towards aromatic solvents with minimum gel concentrations approaching 4 mg mL(-1). Their gelation ability is found to be highly dependent on the nature of the amino acid compositions, the amino acid layer-block sequence within the dendritic architecture and the nature of the focal-point functionality. IR spectroscopic analysis indicates that gelation is induced by intermolecular hydrogen bonds. Circular dichroism studies suggest the formation of hierarchical chiral structures in the gel state, although the existence of chiral morphologies could not be observed by scanning electron microscopy.

New Concepts in Tetrathiafulvalene Chemistry

Tetrathiafulvalene (TTF) and its derivatives were originally prepared as strong electron-donor molecules for the development of electrically conducting materials. This Review emphasizes how TTF and its derivatives offer new and in some cases little-exploited possibilities at the molecular to the supramolecular levels, as well as in macromolecular aspects. TTF is a well-established molecule whose interest goes beyond the field of materials chemistry to be considered an important building block in supramolecular chemistry, crystal engineering, and in systems able to operate as machines. At the molecular level, TTF is a readily available molecule which displays a strong electron-donor ability. However, its use as a catalyst for radical-polar crossover reactions, thus mimicking samarium iodide chemistry, has only recently been addressed. Important goals have been achieved in the use of TTF at the macromolecular level where TTF-containing oligomers, polymers, and dendrimers have allowed the preparation of new materials that integrate the unique properties of TTF with the processability and stability that macromolecules display. The TTF molecule has also been successfully used in the construction of redox-active supramolecular systems. Thus, chemical sensors and redox-switchable ligands have been prepared from TTF while molecular shuttles and molecular switches have been prepared from TTF-containing rotaxanes and catenanes. A large synthetic effort has been devoted to the preparation of the so-called organic ferromagnets, many of which are derived from TTF. The main task in these systems is the introduction of ferromagnetic coupling between the conduction electrons and localized electrons. TTF has also played a prominent role in molecular electronics where TTF-containing D-sigma-A molecules have allowed the preparation of the first confirmed unimolecular rectifier. Recently, it has been confirmed that TTF can display efficient nonlinear optic (NLO) responses in the second and third harmonic generation as well as a good thermal stability. These findings can be combined with the redox ability of TTF as an external stimuli to provide a promising strategy for the molecular engineering of switchable NLO materials. Fullerenes endowed with TTF exhibit outstanding photophysical properties leading to charge-separated (CS) states that show remarkable lifetimes.